An 18-year-old who has been in jail since February for making an online comment about 'shooting up a school full of kids' is been on suicide watch because he doesn't believe he will ever be released, his father reveals.

Justin Carter faces eight years in prison if he is convicted of making 'terroristic threats,' a felony.

Carter, who lives near an elementary school, was arrested after he wrote: 'I'm going to go shoot up a school full of kids and eat their still beating hearts jk lol' only two months after the Sandy Hook school massacre.

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Arrest: Justin Carter could faces up to ten years in prison for joking about carrying out a school massacre

Overreaction: Jack Carter says his son was never a threat to anyone and simply made a terrible, stupid joke

Jack Carter told CNNthat his son is getting desperate after five months behind bars.

'He's very depressed, very scared, and ... concerned that he's not going to get out,' Mr Carter said. 'He's pretty much lost all hope.'

Mr Carter maintains that his son's comment was a joke - albeit a poorly-timed, terrible joke.

Mr Carter also claims his son has been subject to abuse by other detainees and solitary confinement while behind bars.

'Without getting into the really nasty details, he's had concussions, black eyes, moved four times from base for his own protection,' Mr Carter said.

'He's been put in solitary confinement, nude, for days on end because he's depressed. All of this is extremely traumatic to this kid. This is a horrible experience.'

Regrets: In 2013, a Texas teenager was jailed after writing on Facebook: 'I'm going to go shoot up a school full of kids and eat their still beating hearts' only two months after the Sandy Hook school massacre

Game over: Justin had been playing League of Legends when he got into an argument with an online player

Mr Carter has previously said the punishment that authorities are seeking doesn't fit the crime.

'These
people are serious. They really want my son to go away to jail for a
sarcastic comment that he made,' Justin's father, Jack Carter, said.

Although
the teenager, who turned 19 in prison, added 'lol' (laughing out loud)
and 'jk' (just kidding) to his post, a woman from Canada who saw it
reported Justin to police after finding out that he lived near an
elementary school.

Mr
Carter is now campaigning to have his son released, and wants to teach
teenagers about the dangers of posting comments on social media.

'Justin was the kind of kid who didn't
read the newspaper. He didn't watch television. He wasn't aware of
current events. These kids, they don't realize what they're doing. They
don't understand the implications. They don't understand public space,' he told KHOU.

His son first got into trouble in February after he and a friend had been playing League of Legends.

Mr Carter said: 'Someone had said something to the
effect of "Oh you're insane, you're crazy, you're messed up in the
head," to which he replied "Oh yeah, I'm real messed up in the head, I'm
going to go shoot up a school full of kids and eat their still, beating
hearts.'

He added that his son had made it clear that the comment was made in jest.

A woman in Canada contacted the police after a Google search showed Justin's last known address was close to Wooldridge Elementary School in Austin.

Campaign: Justin's father, Jack Carter, started an online petition to raise awareness about the case

Justin was charged with making a terroristic threat and faces a trial on July 1.

A spokesman for Austin police said that after recent events statements such as the one Justin made are taken seriously.

The teenager's family have set up an online petition - Release Justin Carter - to raise awareness of his case.